Tag: refraction of light at plane surfaces

Questions Related to refraction of light at plane surfaces

When a ray of light strikes the glass slab at $90^{\circ}$, it is seen that it does not deviate from its path. In such a situation :

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. angle of incidence is zero

  2. angle of refraction is zero

  3. both(a) and (b)

  4. none of these

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Correct Option: C
Explanation:

 If the rays of light are incident upon the glass surface perpendicularly, or at 90 degree angle to the surface, the rays will pass through without changing direction. In this case, the angle of incidence and angle of refraction are always zero.
Hence, the option A and B are correct.

The velocity of light in air is $3\times 10^{10} cm/\sec$. If the refractive index of glass with respect to air is $1.5$, then velocity of light in glass is

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. $2\times 10^{10} cm/\sec$

  2. $4.5\times 10^{10} cm/\sec$

  3. $3\times 10^{10} cm/\sec$

  4. $1\times 10^{10} cm/\sec$

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Correct Option: A

A bird in air looks at a fish vertically elow it and inside water. X is the height of the bird above the surface of water and Y the depth of the fish below the surface of water if refractive index of water with respect to air is $ \mu $. The distance of the fish as observed by the bird is 

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. X + Y

  2. $ X + Y/ \mu $

  3. $ \mu X + Y $

  4. $ \mu X + \mu Y $

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Correct Option: C

A thin film of a liquid with refractive index $4/3$ produces interference pattern when light of wave length $450\ nm$ is incident normally. The minimum thickness of the film is approximately.

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. $1.68\times 10^{-7} m$

  2. $5.22\times 10^{-7} m$

  3. $4.5\times 10^{-7} m$

  4. $1.25\times 10^{-7} m$

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Correct Option: C

Point like object is observed using microscope angle subtended by objective with object is $20^{\circ}$. If oil of refractive index $1.4$ is kept between object and objective, numerical aperture will be ________.

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. $0.24$

  2. $0.48$

  3. $2.4$

  4. $4.8$

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Correct Option: C

A ray of light passes from a medium L to a medium K. No refraction of light occurs if the ray of light hits the boundary of these two media at the angle of incidence equal to ...............

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. $30^{\circ}$

  2. $90^{\circ}$

  3. $0^{\circ}$

  4. $120^{\circ}$

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Correct Option: B
Explanation:

If a light is an incident at an angle of $90^{o}$ it will go straight again making an angle of $90^{o}$ with the normal it doesn't depend on medium.
so the angle of incidence is $90^{o}$
A because if an angle of incidence is 90°, it means the light is propagating along the interface separating the two media. In this case, the light does not enter the second medium and so we can not talk about the angle of refraction. The angle of refraction can also be regarded as 90°.

The critical angle for refraction from medium -1 to air is ${ \theta  } _{ 1 }$ and that from medium -2 to air is ${ \theta  } _{ 2 }$. If medium -2 is denser then medium -1. Find the critical angle for refraction from medium -2 to medium. 

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. ${ sin }^{ -1 }(\frac { { sin\theta } _{ 2 } }{ { sin\theta } _{ 1 } } )$

  2. ${ sin }^{ -1 }(\frac { { sin\theta } _{ 1 } }{ { sin\theta } _{ 2 } } )$

  3. Both A and B

  4. None of these

Show answer
Correct Option: B
Explanation:

From medium 1 to air


$\eta _1sin\theta _1 = \eta _2sin\theta _2$

 here $\eta _2$ = 1 (air)

$\eta _1 = \frac{1}{sin\theta _1}$

Similarly for medium 2 to air

$\eta _2 = \frac{1}{sin\theta _2}$

Now from medium (2) to (1)

$\eta _2sin\theta _2 = \eta _1sin\theta _2$

$sin\theta _c = \frac{sin\theta _2}{sin\theta _1}$

$\theta _c = sin^{-1}(\frac{sin\theta _2}{sin\theta _1})$

If any two media are optically exactly the same then; when light passes from one medium to another then:

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. No bending occurs

  2. Sometimes it can bend

  3. Compete bending occurs

  4. None

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Correct Option: A
Explanation:

Since, both media are optically same, there is no difference in the absolute refractive indices of the two media.

        Hence, light passes through them undeviated that is no bending occurs.

Answer-(A)

Light, which is travelling along a normal, is ............ refracted

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. Partially

  2. Completely

  3. Not

  4. All

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Correct Option: C
Explanation:

The light travelling along normal don't get refracted and passes undeviated.


Answer-(C).

A vertical ray of light strikes the horizontal surface of water. What will be the angle of incidence?

conditions for a light ray to pass undeviated refraction of light at plane surfaces physics

  1. $90^{\circ}$

  2. $100^{\circ}$

  3. $180^{\circ}$

  4. $0^{\circ}$

Show answer
Correct Option: D
Explanation:

Angle of incidence$(i)$ is the angle between incident ray and normal.

Here, ray strikes the surface normally, hence $i=0^{o}$

Answer-(D).